Coal Soot Darkened, Melted Glaciers During Industrial Revolution

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Soot billowing across Western Europe during the Industrial
Revolution may have caused the abrupt and unexpected retreat of
European glaciers during a climatically cool period in the 19th
century, new research suggests.

Mountain glaciers in the European Alps retreated by an
average of nearly 0.6 miles (1 kilometer) between 1860 and 1930.
This period falls at the end of Europe's so-called Little Ice
Age, when temperatures dipped below average by about 1.8 degrees
Fahrenheit (1 degree Celsius) across much of the continent.

Scientists have long struggled to identify a cause for this
surprising retreat, but had been unable to find a suitable answer
in the climate record. Now, researchers based at NASA's Jet
Propulsion Laboratory in Pasadena, Calif., have honed in on the
potential anthropogenic — or human-induced — causes of the
retreat. The researchers focused on the potential impact of
particulate carbon, or soot, on snow melt. Soot was a major form
of pollution at the time of the melt, given the prevalence of
coal burning in that era. [ In
Images: Tracking a Retreating Glacier ]

When soot settles on snow in large enough quantities, it creates
a dark, heat-absorbent film on the otherwise reflective white
surface of the snow. This causes the surface to absorb
significantly more heat than it otherwise would, which eventually
thins the snow down to the glacial ice that sits below the
surface layer, causing further retreat.

To examine whether this effect would have been strong enough to
induce the abrupt glacial retreat in the European Alps, the team
analyzed ice cores collected from several European mountain
glaciers and measured the levels of soot in various ice layers.
The researchers used these measurements to estimate the
quantities of soot that would have settled on glaciers lower in
the Alps during the Industrial Revolution, and then entered this
data into a computer model of glacial behavior.

They found that the soot could, in fact, have had a strong enough
effect to heat and melt the snow at the rate
recorded.

"This study uncovers some likely human fingerprints on our
changing environment," Waleed Abdalati, a researcher at the
University of Colorado and an author on the paper, said in a
statement. "It's a reminder that the actions we take have
far-reaching impacts on the environment in which we live."

The research appeared in the Sept. 2 issue of the journal
Proceedings of the National Academy of Sciences.